CMS ECAL Protvino in the PANDA barrel Electromagnetic Calorimeter (first look) V.A. Kachanov.
The CMS ECAL Laser Monitoring Systembornheim/html/slides_siena_2008_bornheim.pdf · October 3, 2008...
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IPRD 2008 11th Topical Seminar On Innovative Particle and Radiation Detectors Adi Bornheim Adi Bornheim California Institute of Technology California Institute of Technology On behalf of the CMS ECAL Collaboration On behalf of the CMS ECAL Collaboration Siena, October 3, 2008 Siena, October 3, 2008 The CMS ECAL Laser Monitoring System
Transcript of The CMS ECAL Laser Monitoring Systembornheim/html/slides_siena_2008_bornheim.pdf · October 3, 2008...
IPRD 2008 11th Topical Seminar On Innovative Particle and Radiation Detectors
Adi BornheimAdi BornheimCalifornia Institute of TechnologyCalifornia Institute of Technology
On behalf of the CMS ECAL CollaborationOn behalf of the CMS ECAL Collaboration
Siena, October 3, 2008Siena, October 3, 2008
The CMS ECAL Laser Monitoring System
October 3, 2008 A.Bornheim - The CMS ECAL Laser Monitoring System 2
90 Tons of Lead-Tungstate
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CMS is building a high resolution Crystal Calorimeter (ECAL) to be operated at LHC in a very harsh radiation environment.
Barrel resolution design goal :
Current effective resolution goal : <0.5% for energies above 100 GeV
Calibrating and maintaining the calibration of this device will be very challenging.Hadronic environment makes physics calibration more challenging
PWO4 Crystals change transparency under radiation.
The damage is significant (few % - up to ~5 % for CMS ECAL barrel radiation levels) compared to the desired constant term (0.5 %).
The dynamics of the transparency change is fast (few hours) compared to the time scale needed for a calibration with physics events (days - weeks - month).
⇒ Compensate by monitoring the change with a laser monitoring system.
Introduction
EE /2.0%55.0/%5.2 ⊕⊕
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Radiation Reduces transmittance in the blue and green, peak of PWO4 emission spectrum
Effect is dose rate dependent. Monitoring relative loss of PWO4
transmittance with pulsed laser light.
For the expected dose rate at CMS barrel (15 rad/hour), typical transmittance loss is at a level of up to ~5%.
Radiation Effects on PWO4 Transparency
Almost no effect in the red wavelength range.
Monitor with red light to separate out possible variations in the light distribution system and the readout chain.
Approx. PWO emission spectrum
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PWO4 Transparency Change Characteristics
Crystal light yield changes under irradiation. Change is dose rate dependent.
Crystal light yield change under irradiation is linearly correlated with longitudinal transmittance (transparency).
Magnitude of the transparency change is crystal dependent.
Transparency change recovers at room temperature. Recovery time is crystal dependent with two time constants, one of few 10 hours and one >1000 hours.
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Damage and Recovery in a ’LHC Cycle’
⇒ Damage-recovery cycle in sync with the ~12 hour LHC fill cycle
Test Beam Data
Recovery RecoveryDamage Damage
Simulation
Depends on :Radiation level (η, Luminosity)Crystal characteristics
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In-Situ Monitoring & LHC Bunch Train
Abort Gap
Abort gaps occur at ~10 kHz - Laser pulses at ~100 Hz ⇒ Use ~1% of gaps. Measure transparency of all crystals from one half-module at a time. 600 laser shots for
one transparency measurement. Laser pulse latency ~4 µs
⇒ Scan entire ECAL every 20 minutes
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On-Detector Monitoring System
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Very stable PN-diodes used as reference system Each Level-1 Fan-out is seen by 2 PN diodes, each PN diode sees
2 Level-1 Fan-out, 10 PN diodes per SM SM are illuminated one half at a time, 88 LM for full ECAL Barrel crystals front illuminated, endcap rear illuminated Precision charge pulsing system for electronics calibration
APDPN
APD
VPT
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Ti:Sapphire Laser with Two Wavelengths
Tunable Ti:S
Nd:YLF Pump
10 kW
100 mW
440 nm500 nm700 nm800 nm
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Long Term Laser Performance
Changes in the pulse shape of the laser are the larges systematic effect.
⇒ Precise control of laser performance is of utmost importance.
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Light Distribution System
1.0151.01
1.0051.0
0.9950.99
0.985
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Endcap LED Pulser System
ECAL EE equipped with additional LED pulser system.
Provides additional wavelength (~600 nm) and allows high rate pulsing.
Complementary to laser system.
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Mean before and after correction for laser pulse shape changes : 0.180 % 0.088 % Peak before and after correction for laser pulse shape changes : ~0.170 % ~0.05 %
Monitoring System Performance - Stability
Typically ~0.1 % long term stability in real environment. This includes the stability of the entire readout chain - temperature, HV, etc.
⇒ We can measure the crystal transparency with better than 0.1 %.
Stability : RMS of the measured APD/PN values over a period of 4 weeks.
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Laser Light Loss – Electron Signal Loss
signal from Laser signal from Laser
sign
al fr
om B
eam
(esi
gnal
from
Bea
m (e
-- ) )
a
a
slope :α = 1.55
About 100 About 100 α-parameter extractions with final hardware on 35 barrel and 41 endcap crystals have been performed.parameter extractions with final hardware on 35 barrel and 41 endcap crystals have been performed.
⇒ At startup use same parameters for all crystals from one producer.An in-situ determination of α is under consideration.
α
Dispersion of α for 35 BTCP crystals
20022003
2004 (fall)
2004 (spring)
2006 (center)
2006 (neighbor)
mean = 1.538σ/mean ≈ 6%
# C
ryst
als
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Correcting Transparency Change
⇒Transparency change can be corrected to better than 0.1 %
⇒Energy resolution is fully restored to pre-irradiation level
Single irradiation cycle effects :
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ECAL DAQTTCci
Laser Monitoring Online Data Flow
ECAL
Other SubdetectorsLaserSystem
CMS Global Trigger
EMTC
Calibration Events
Online PCs
Readout Units
Filter Farm
Storage Managers
Disk BufferLaserFarmHLT Filter
Offline
⇒ Laser data acquisition fully integrated in the CMS DAQ and data flow.
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Running experience in CMS
ECAL Laser Farm Raw data rate for laser monitoring is 4 Mb/s.
Data is sampled by DQM and analysed in detail in a quasi-online fashion.
Aim to have transparency corrections available on the level of 0.1% at the end of a LHC fill.
So far mostly used for commissioning, debugging and timing studies of ECAL.
Stability studies are under way.
CMS Online DQM Plots Quasi Online Analysis Plots
⇒ Regular data taking has commenced, aiming to monitor at design precision.
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Summary
CMS ECAL Laser Monitoring System has been installed and commissioned in the final detector.
All performance criterions have so far been achieved.
Next step is to validate the stability of ECAL response to the level of 0.1 % over several weeks without irradiation.
Then, operating the system and follow the crystal transparency on the level of 0.1% over 10 years.
